Measurement of the ability of a patient's blood to coagulate in timely and effective fashion is crucial to certain surgical and medical procedures. Blood coagulation analyzer instruments have been known since Helmut Hartert developed them in Germany in the 1940's. A U.S. Pat. showing the background and continued development of the Hellige line of such instruments is No. 3,714,815.
In such instruments, a small stainless steel cup is pre-warmed to body temperature. A sample of whole blood is placed into the cup. A cylindric pin suspended on a thin wire is lowered into the cup and the blood sample, which then is covered with mineral oil. The cup is oscillated gently, over about 10 seconds, back and forth through a small angle, about 4 degrees, around its vertical axis. As the blood coagulates or clots, elements in the blood link the cup and the pin surfaces together, so the pin too begins to oscillate. The oscillations of the pin are detected by reflected light beams, magnetically, or otherwise. Ultimately the pin and the cup oscillate together, if the clot is strong and does not break up.
Delay in onset of the clot, weakness of the clot, or breaking up of the clot are shown clearly in a real-time plot of the movements of the pin. The plot may be expressed by mathematical factors characterizing its shape.
Blood may be contaminated with hepatitis virus, AIDS virus, and other infectious agents dangerous to the personnel operating the blood test equipment. Cleaning of the surfaces contacting the blood necessarily brings such personnel into contact with the blood on the surfaces, particularly where the blood has congealed. Cleaning and drying must nonetheless be thorough, and the surfaces must not be scratched, to ensure accuracy of subsequent test results.
Although the desireability of use of disposable blood coagulation test implements has been recognized generally, no practicable structures for disposable pins and/or cups for use in blood coagulation test equipment have been proposed. Merely replicating the conventional stainless steel pins and cups in plastic does not overcome problems such as actually sinking the suspended pin in the blood, avoiding breakage of the thin shaft of the pin where it is inserted into the suspension and measuring assembly, and transferring adequate heat to the blood in the cup.